The present invention relates to the art of permanently joining metal and plastic parts and, more particularly, to novel structure of annular metal fittings and methods of affixing the same to an external, cylindrical surface of a rigid plastic part.
One common method of joining a metal piece to a rigid plastic part is the so-called ultrasonic welding process. By imparting high frequency vibrations causing friction between the metal and plastic, localized softening is induced in the plastic, allowing it to flow around or into the metal part. The plastic hardens again very soon after the vibrations are stopped, and the two parts are, in effect, permanently joined.
It is sometimes desirable to place an annular metal fitting on the outside of a plastic tube, or other part having a cylindrical external surface. In U.S. Pat. Nos. 2,967,067 and 2,787,480, for example, a plastic hose or tube is provided with an external fitting of metal having annular teeth sloped inwardly in the direction of insertion of the fitting on the tube. The plastic is of the pliable or resilient type which allows a force fit, the inside diameter of the fitting at the crests of the teeth being somewhat smaller than the external diameter of the plastic tube or hose.
The particular structure of the fittings used for insertion by force fit over a resilient plastic tube, however, are not suitable for joining with a rigid plastic part, by ultrasonic welding or other known processes. It has been the usual practice to use cylindrical parts of rigid or "engineering" type plastics without the benefit of longer wearing external metal fittings because of the difficulty in joining the parts. Although it is more economical to form many parts from molded plastic rather than metal, the useful life of the part may be quite short, particularly where it is subject to friction or abrasion.
It is a principal object of the present invention to provide a novel configuration of annular metal fitting which facilitates permanent connection thereof to a rigid plastic part.
A further object is to provide a method of forming an annular metal fitting and permanently connecting it to an external cylindrical surface of a rigid plastic part.
Other objects will in part be obvious and will in part appear hereinafter.